A standard conveyor-belt system such as used in a mining operation to move ore or the like comprises an endless belt spanned between at least two rollers and having an upper stretch that supports the load and a lower stretch. The downstream roller at least is driven to advance the upper belt stretch in a longitudinal transport direction. Further rollers are provided under the upper stretch at least in long installations to provide support for the upper stretch.
When the system is carrying substantial loads and/or is quite long it is necessary either to provide a succession of belts with the downstream end of each upper stretch passing its load to the upstream end of the next downstream belt, or to provide intermediate drives which engage the upper stretch and pull it in the transport direction. There is an upper limit to the possible length as the friction losses between drive rollers and the belt are substantial, especially when the belt only tangentially engages a roller.
These problems are particularly irksome when used in an underground mining operation as detailed in "Hebezeug und Fordermittel" (18, 1798, pages 76-80) with respect to the use of intermediate drives. The size of such intermediate-drive units is excessive in the tight spaces in mines, and servicing them is almost impossible.
It has accordingly been suggested to imbed permanent magnets in the longitudinal edges of a conveyor belt and to provide C-section stators defining grooves in which these edges run, thereby forming a linear magnetic motor assembly. Synchronizing the driving forces on opposite edges of the belts proves very difficult, and the stators quickly wear out due to entry of grit into the space between the belt and the stator.